FREQUENT INVOLVEMENT OF THE INTERNAL CUFF SEGMENT IN CAPD PERITONITISAND EXIT-SITE INFECTION - AN ULTRASOUND STUDY

Background. The extent of involvement of the subcutaneous Tenckhoff ca theter tract in CAPD peritonitis and catheter-related infections is of major therapeutic importance. By definition, both peritonitis and exi t-site infections do not involve the catheter tract. However, diagnosi s of these infections as well as the more sinister tunnel infection is based mainly on clinical signs. Methods. We examined the usefulness o f ultrasound examination (US) of the catheter tract in delineating cat heter-related (exit-site and tunnel) infections, and their relationshi p to each other and to peritonitis. CAPD patients with no evidence of peritonitis or catheter-related infections for 6 months prior to exami nation served as controls. US were performed by one of two experienced radiologists using the Acuson 128XP/10 scanner with a 7-MHz linear tr ansducer. A positive US was defined as an area of hypoechogenicity (in dicative of fluid collection) >2 mm in width along any portion of the catheter tract. Findings were localized into segments (S) as follows. S1, limited to external cuff; S2, intercuff segment adjacent to the ex ternal cuff; S3, intercuff segment adjacent to the internal cuff; S4, limited to the internal cuff; and S5, involvement extending throughout the catheter tract. Results. Between March 1993 and January 1995, 39 CAPD patients, all with a double-cuff straight Tenckhoff catheter with the exit site situated above the point of entry into the peritoneum w ere studied. A total of 56 US were performed divided among 26 episodes of peritonitis, four tunnel infections, 13 exit-site infections, and 13 controls. There were 30 positive US distributed among 16 peritoniti s, four tunnel, eight exit site infections and two control patients. T he two positive controls went on to develop peritonitis within 1 month of the US. The majority of the US findings (13/16 in episodes of peri tonitis and 5/8 exit site infections) were localized to segment 4, tha t is, to the internal cuff region. Apart from a significant increase i n width in all infected segments versus a normal tunnel, no difference s in size were seen between peritonitis, exit-site, or tunnel infectio ns, nor were there ally differences in size and localization in these infections when comparing the offending organism (Gram-positive, negat ive, or culture negative). Conclusions. We conclude that peritonitis a nd exit-site infections are frequently accompanied by involvement of t he catheter tract. The localization of infection to the internal cuff region in cases of exit-site infection probably occurred as a result o f downward migration along the catheter tract. This supports the notio n that ideally the exit site should be pointing caudally or that the p eritoneal catheter have a swan-neck configuration. With regard to peri tonitis, infection within the peritoneal cavity appears to extend and involve the internal cuff region. Thus both the internal and external cuffs do not seem to pose an effective barrier against the spread of i nfection. Based on our data, we recommend that US be performed as a ro utine investigation in all cases of exit-site infection and in cases o f refractory or relapsing peritonitis.